The relationship between magneto-optical properties and molecular chirality

Satoshi Wada,Yasuhiro Morisaki,Takayuki Nakanishi,Koji Fujita,Koji Fushimi,Katsuaki Konishi,Yoshiki Chujo,Yuichi Kitagawa,Katsuhisa Tanaka,Yasuchika Hasegawa

doi:10.1038/am.2016.17

Satoshi Wada, Yasuhiro Morisaki + Show 8 more

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https://doi.org/10.1038/am.2016.17

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Abstract

The chiral nonanuclear Tb(III) clusters [Tb9(sal-(R)-Bt)16(μ-OH)10]+[NO3]− (Tb-(R)-Bt: sal-(R)-Bt=(R)-2-butyl salicylate) and [Tb9(sal-(S)-Bt)16(μ-OH)10]+[NO3]− (Tb-(S)-Bt: sal-(S)-Bt=(S)-2-butyl salicylate) were found to exhibit a unique magneto-optical property: the Faraday effect. The clusters were composed of 9 Tb(III) ions bridged by 10 μ-OHs and 16 chiral salicylic acid esters. The Faraday rotation angle of Tb-(R)-Bt was greater than that of Tb-(S)-Bt, indicating that the Faraday effect was affected by the chirality of the Tb(III) clusters. The chiroptical properties of the Tb(III) clusters were estimated using circular dichroism and circularly polarized luminescence. In this study, a new finding concerning chiral magneto-optical properties was investigated. By pairing chiral organic ligands with rare-earth clusters, scientists have gained surprising insights into magneto-optical material design. Many optical telecommunication devices use the Faraday effect — a means of rotating the polarization of light using magnetic fields — to prevent unwanted light transmissions. Now, Yasuchika Hasegawa from Hokkaido University in Japan and co-workers have observed the first-ever correlation between the Faraday effect and molecular chirality. The Faraday effect is traditionally viewed as being insensitive to natural optical activity such as chirality. But the team's previous investigations, which showed organic ligands influenced promising Faraday materials known as terbium glasses, inspired them to challenge long-held assumptions. They synthesized nine-membered terbium clusters and complexed them with chiral salicylate ligands. Different ligand chirality categorically affected the Faraday rotation angles — an effect that may arise from terbium's large transition magnetic dipole. Naturally occurring and magnetically induced optical activities (the Faraday effect) have contributed to our understanding of molecular electronic states, and have also had various applications in photonics. It has been generally considered that the Faraday effect is not affected by natural optical activity originating from chirality. Herein we describe for the first time a relationship between the Faraday rotation angles and chirality in a chiral lanthanide cluster. This finding provides new insights into the design of next-generation molecular Faraday materials and may lead to the development of a novel area of study within the field of chiral science.

Highlights

The Faraday effect, a magneto-optical property, has received significant attention with regard to applications of magneto-optical materials
Inorganic lanthanide compounds such as Tb(III)-doped borosilicate glasses and Tb(III) garnet ceramics exhibit large Faraday effects because of the large angular momentum of the 4f electron, and such materials have been used to construct optical isolators employed in optical communication systems.[2,3,4,5]
We recently described nonanuclear Tb(III) clusters coordinated with salicylate ligands that are a new type of lanthanide material exhibiting a large Faraday effect.[6]

Summary

Introduction

The Faraday effect, a magneto-optical property, has received significant attention with regard to applications of magneto-optical materials. The Faraday effect originates from the Zeeman splitting of electronic states based on the angular momentum of electrons in the material Inorganic lanthanide compounds such as Tb(III)-doped borosilicate glasses and Tb(III) garnet ceramics exhibit large Faraday effects because of the large angular momentum of the 4f electron, and such materials have been used to construct optical isolators employed in optical communication systems.[2,3,4,5]. We identified a further unique property of these clusters: the rotation angles were different depending on the organic ligands This finding has the possibility to lead to new molecular designs for Faraday effect materials based on the type of the organic ligands

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